Date of Award

2010

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Department

Chemical and Biochemical Engineering

First Advisor

Jesse Zhu

Abstract

Powder coatings have emerged as an alternative to the conventional liquid coatings when environmental regulations become stricter every year. The advantage of powder coatings mainly renders to their solvent-free formulations, because solvent(s) used in liquid coatings are to be evaporated to environment contributing to the total volatile organic compounds (VOCs) emissions. Although advantageous, until recently, powder coating was not able to provide surface finishes comparable to the liquid coatings. However, when ultrafine powders (particularly, in the size range of 15-25 µm) becomes flowable with the aid of nano-additive(s), ultrafine powder coatings (UPCs) came into business with its thinner and smoother films well-comparable to the liquid coatings. Thus UPC offers environmentally friendly alternative to the coating industries having applied to develop many functional coatings.

Ultrafine powder coating (UPC) technology has been utilized to develop superhydrophobic powder coatings that mimic lotus leaf surfaces and exhibit water contact angles (CAs) of over 160° and sliding angle (SA) of less than 5° on the coated substrates. Water droplets tend to be very unstable on these surfaces so that they run away from the superhydrophobic surfaces even with the slightest inclination. This unique phenomenon is attributed to the double-scale micro-/nano hierarchical structures that have been successfully fabricated on such surfaces just by incorporating nano-sized hydrophobic additive(s) in the coating formulations. Thus the solvent-free UPC technique has offered simple but environmentally friendly solution in developing superhydrophobic surfaces that could be used as self-cleaning surfaces.

Ultrafine powder coating (UPC) technique has been employed to develop polymeric biocompatible powder coatings enriched with nano-Ti02 with varying degree of nanoroughness ranging from -37 nm to -260 nm. The developed coatings have been assessed for their biocompatibility when human mesenchymal cells were cultured on them. Cells attached spread and expressed Runx2 and Collagen Type Ion these biocompati ble coatings. Interestingly, they performed even better than commercially pure titanium (cpTi) when their nanoroughness could be maintained below -50 nm. UPC has been able to tune up the nanoroughness of the developed coatings without changing anything in the existing processes, rather by changing amount of the constituents in the coating formulations. Thus UPC could possibly replace the traditional techniques (plasma treatment, sputter-coating or vapour deposition) to develop bioactive coatings for medical devices with offering simple and inexpensive coating method.

Ultrafine powder coating (UPC) technique has also been used to apply flow-modified glass ionomer cement (GIC) powders onto exposed dentine surfaces to occlude exposed dentinal tubules that could effectively treat dentine hypersensitivity. Proprietary ultrafine GIC powders, (Ketac-Cem® and Fuji I® ) have been processed with appropriate amounts of nano-sized Ah03 to improve their flowability before applying them to the dentine sections by using UPC process employing Corona spraying gun. With this powder spraying technique, dentinal tubules have been occluded as deep as -1 mm µm, in some instances. Such deeper dentinal tubule occlusion renders superiority over any other existing technique (i.e., highest penetration depth was revealed in the literatures is -270 µm). Moreover, UPC technique showed a higher proportion of tubules filled. Thus, UPC could enter into the treatment of dentine hypersensitivity.

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Creative Commons Attribution 4.0 License
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